Abstract

Most individual insect migrants have only a short time ‘window’ for migration (just a few nights) and comparatively slow airspeeds. Thus, to achieve long-range displacement into temporary breeding habitats, migrants must hitch a ride on fast-moving, high-altitude winds [1]. We recently demonstrated that the migratory noctuid moth Autographa gamma has evolved a compass mechanism which facilitates the successful return of autumn migrants from the United Kingdom to their winter ranges further south via the selection of favourable high-altitude winds [2]; this was the first convincing evidence of such a mechanism in insects that migrate predominantly at high altitudes. As pointed out in a commentary on that work [3], the question of whether or not a similar mechanism promotes northwards migration of such insects during the spring remained unanswered — we do not know if there is a reversal of the migrants' preferred compass orientation according to season. Here, studying A. gamma once again, we report the first evidence that a nocturnal migrant moth controls the direction of both its spring (‘forward’) and autumn (‘return’) high-altitude migrations, and that it also optimises its flight-altitude and compensates for cross-wind drift in a similar manner in both directions